In a conventional cellular wireless system, a base station communicates directly with a user terminal. If two antennas are available at the base station, a space time block code (STBC), such as an Alamouti STBC, may be used to obtain diversity gain, thus improving the quality of the received signal. A multihop network differs from a conventional cellular network in that one or more relays may be included in the path between a base station and a user terminal. Multihop diversity, sometimes known as cooperative relaying, combines the signals from the source (e.g., base station) and a relay at the destination (e.g., user terminal) to improve the quality of the received signal. The purpose of a multihop system is to enhance the signal quality at the destination (base station on the uplink and user terminal on the downlink) in comparison with a conventional cellular wireless system.
A number of alternative cooperative relaying schemes have been proposed but these involve multiple relays acting in parallel in each path, which means more relays are required, resulting in a higher network cost. Space time coding has also been proposed for use with multihop systems but schemes known to the author involve multiple antennas at the base station and the relays, and sometimes at the user terminal as well. While the use of multiple antennas at the base station is practical, multiple antennas at the relay would mitigate against many deployment options which are attractive for other reasons (e.g., cost of deployment, access to sites, etc.). The use of multiple antennas at the user terminal is something that terminal manufacturers have resisted in their efforts to reduce cost and size of the terminal.